The process for fabricating a semiconductor device employs an apparatus for cleaning a semiconductor wafer (hereinafter referred to simply as wafer) on whose surface is provided a thin film circuit pattern.
A conventional apparatus for cleaning a wafer is illustrated in FIG. 1. The apparatus includes a spin chuck 10 for substantially horizontally supporting a wafer (W) by suction and rotating it, and a treatment liquid supply nozzle 30 arranged above the rotational center of the spin chuck to supply a cleaning or treatment liquid on the surface of the wafer (W).
Firstly, a motor not shown drives the spin chuck 20 to rotate the wafer (W) at a given speed. When the rotation is stabilized, the cleaning or treatment liquid is ejected from the nozzle 30 on the surface of the wafer (W) at a given speed to clean or treat it.
If the wafer (W) has both front and back surfaces useful, the wafer (W) is reversed by a reversing mechanism to clean or treat the back surface through the same process after the front surface has been cleaned or treated.
However, although cleaning both front and back surfaces of a wafer, such conventional cleaning apparatus is so designed to make it difficult to clean the edge of a wafer. As the size of a wafer is increased, it becomes more important to remove polymeric residual present in its edge, and there has been conventionally proposed a process of cleaning the edge employing a belt, brush, etc.
One of the processes of cleaning the edge of a wafer employing a brush is proposed in U.S. Pat. No. 5,976,267 granted to Timothy, et al.
This patent, as shown in FIGS. 2A to 2C, a wafer 250 is cleaned by the upper brush 202 moving through a scrubber in the direction indicated by an arrow 701. The lower brush 302 is arranged beneath the wafer 250 directly opposed to the upper brush 202. The upper and lower brushes 202 and 302 are provided with motors to rotate them as well as edge brushes 220 and 320. Two rolls 501 and 502 are provided contacting the side of the wafer at two positions so as to rotate the wafer counterclockwise as indicated by an arrow 702. The rolls 501 and 502 are rotated respectively by stepper motors 503 and 504. The wafer 250 has all its surfaces including the edge cleaned while rotating between the brushes 202, 302, 220 and 320.
Removal of contaminating particles may be facilitated by a water ejector 380 arranged so as to eject water in or near a contact position between the edge brushes 220 and 320 and the wafer, as shown in FIG. 2C. Such a water ejector may be positioned so as to make water flow from a plane aligned with the rotational shaft of the wafer to contact the regions between the wafer and the side scrubbing mechanism. In this case, water may simply move away the particles detached from the wafer by the side scrubbing mechanism, or if having a pressure sufficiently large, directly remove the particles from the wafer. The water ejector may be arranged in a proper place by means of a conventional support structure, and is positioned directly above the wafer in the drawings. The water ejector has a diameter of ⅛ to 1/16 inch, making a water ejection in the form of a sector blade. The edge brushes have bristles 222 and 322 subjected to the ejection of pure water or along with NH4OH or mixture NH4OH/H2O of pure water and NH4OH to prevent the contaminating particles from being accumulated in the bristles 222 and 322 while cleaning the wafer.
However, such conventional apparatus for cleaning the edge of the wafer employs a plurality of rolls and motors for driving the rolls in order to clean the edge of the wafer, and therefore, has a complicated structure increasing the production cost, and the brushes mechanically constructed may produce physical damages on the wafer by contacting, and moreover, the wafer may be re-contaminated by the cleaning liquid contaminated after cleaning the edge of the wafer, lowering the yield rate of wafers.